A case of complete deficiency of total thyroxine-binding globulin (TBG) associated with Graves disease

Doo-Man Kim1, Hyeon Kyu Kim1 & Soon Jib Yoo2

1Department of Internal Medicine, Hallym University College of Medicine, Seoul, Korea, Republic of Korea; 2Department of Internal Medicine, College of Medicine, Catholic University, Seoul, Republic of Korea.

Thyroxine-binding globulin (TBG), the major transport protein for thyroid hormone in circulation, is synthesized in the liver. Complete TBG deficiency was first reported in 1964, and in 1991 a single nucleotide deletion was found in the first base of the codon for amino acid 352 of the common-type TBG molecule. This mutation causes a frameshift in translation and premature termination. Most people with abnormal TBG concentrations are euthyroid. Cases of Graves disease with periodic paralysis and complete deficiency of TBG have rarely been reported.

Allele specific PCR and DNA sequencing of the patient revealed a single nucleotide deletion was found in the first base of the codon for amino acid 352 of the TBG. We treated him with methimazole and followed.